The armed forces of a country are its government-sponsored defense, fighting forces, and organizations. They exist to further the foreign and domestic policies of their governing body and to defend that body and the nation it represents from external and internal aggressors. In broad usage, the terms "armed forces" and "military" are often treated synonymously, although in technical usage a distinction is sometimes made in which a country's armed forces may include both its military and other paramilitary forces. Armed force is the use of armed forces to achieve political objectives.

The study of the use of armed forces is called military science. Broadly speaking, this involves considering offense and defense at three "levels": strategy, operational art, and tactics. All three levels study the application of the use of force in order to achieve a desired objective.

The obvious benefit to a country in maintaining armed forces is in providing protection from foreign threats and from internal conflict. In recent decades armed forces personnel have also been used as emergency civil support roles in post-disaster situations. On the other hand, they may also harm a society by engaging in counter-productive (or merely unsuccessful) warfare. Expenditure on science and technology to develop weapons and systems sometimes produces side benefits, although some claim that greater benefits could come from targeting the money directly.[1][2]